1. Field of the Invention
The present invention relates generally to chemical mechanical polishing (CMP) systems and techniques for improving the performance and effectiveness of CMP operations. Specifically, the present invention relates to CMP systems that use a fixed abrasive polishing pad arranged in a web handling system.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform CMP operations, including polishing, buffing and wafer cleaning. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove excess metallization.
In the prior art, CMP systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to scrub, buff, and polish one or both sides of a wafer. Slurry is used to facilitate and enhance the CMP operation. Slurry is most usually introduced onto a moving preparation surface, e.g., belt, pad, brush, and the like, and distributed over the preparation surface as well as the surface of the semiconductor wafer being buffed, polished, or otherwise prepared by the CMP process. The distribution is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the friction created between the semiconductor wafer and the preparation surface.
FIG. 1 illustrates an exemplary prior art CMP system 100. The CMP system 100 in FIG. 1 is a belt-type system, so designated because the preparation surface is an endless belt 108 mounted on two drums 114 which drive the belt 108 in a rotational motion as indicated by belt rotation directional arrows 116. A wafer 102 is mounted on a carrier 104. The carrier 104 is rotated in direction 106. The rotating wafer 102 is then applied against the rotating belt 108 with a force F to accomplish a CMP process. Some CMP processes require significant force F to be applied. A platen 112 is provided to stabilize the belt 108 and to provide a solid surface onto which to apply the wafer 102. Slurry 118 composing of an aqueous solution such as NH4OH or DI water containing dispersed abrasive particles is introduced upstream of the wafer 102. The process of scrubbing, buffing and polishing of the surface of the wafer is achieved by using an endless polishing pad glued to the belt 108. Typically, the polishing pad is composed of porous or fibrous materials and lacks fixed abrasive particles.
After the polishing pad polishes a limited number of wafers, the surface of the pad is conditioned and cleaned in order to remove the attached abrasive materials of the slurry and the particles removed from the wafer. Subsequent to cleaning and conditioning, the polishing pad will have a significant amount of particles that remain attached to the surface of the polishing pad causing the polishing pad to lose its effectiveness. The polishing pad also loses its effectiveness due to normal wear of the material itself. As a result, the polishing pad must be replaced in its entirety. The removal of the used polishing pad and its subsequent replacement with a new polishing pad is very time consuming and labor intensive. Additionally, the time needed to perform the replacement necessarily requires that the polishing system be taken off-line, which thus reduces throughput.
In view of the foregoing, a need therefore exists in the art for a chemical mechanical polishing system that will enable polishing surface layers of a wafer using a polishing pad that is less expensive to maintain and is more effectively serviced after its use degrades the effectiveness of the polishing.
Broadly speaking, the present invention fills these needs by providing an apparatus and related methods for efficiently polishing layer surfaces of a semiconductor wafer. Preferably, the CMP system is designed to implement a polishing pad strip that is less expensive to maintain and is more efficiently serviced after it loses its effectiveness to polish. In preferred embodiments, the polishing pad is a fixed abrasive polishing pad strip that is connected between a feed roll and a take-up. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a chemical mechanical polishing (CMP) apparatus is disclosed. The CMP apparatus includes a polishing pad strip defined between a first point and a second point. The first point is separate from the second point. Also included is a feed roll having a supply of the polishing pad strip, and the feed roll is configured to define a location of the first point. A take-up roll is further included and it is configured to collect at least a linear portion of the polishing pad strip.
In another embodiment, a chemical mechanical polishing (CMP) apparatus is disclosed. A first roller is situated at a first point and a second roller situated at a second point, such that the first point is separate from the second point. A polishing pad strip is also included and has a first end secured to the first roller and a second end secured to the second roller. The polishing pad strip is configured to provide a surface onto which a substrate to be polished is lowered. Preferably, the polishing pad strip is a fixed abrasive pad and is configured to receive chemicals or DI water so as to facilitate a removal of material from a surface of the substrate.
In still a further embodiment, a method for polishing a semiconductor wafer is disclosed. The method includes providing a polishing pad strip that is to be connected between a first point and a second point. The method then includes applying a tension to the polishing pad strip. Once the desired tension is applied, the polishing pad strip is oscillated between the first point and the second point. The semiconductor wafer is then applied to the oscillating polishing pad strip to commence the CMP process. The method can further include applying a chemical solution to the polishing pad strip before the applying of the semiconductor wafer. Furthermore, the method can include monitoring a linear velocity of the oscillating polishing pad strip, and controlling a setting of the linear velocity of the oscillating polishing pad strip. In addition, the method can include monitoring a tension of the polishing pad strip, and controlling a setting of the tension of the oscillating polishing pad strip.
The advantages of the present invention are numerous. Most notably, instead of a continuous belt polishing pad, a supply of polishing pad strip is provided between a feed roll and a take-up roll in a web handling arrangement. Thus, replacing used portions of the polishing pad strip with fresh portions of the polishing pad strip can be accomplished utilizing minimal effort and in significantly less amount of time. Furthermore, the re-supplying of the polishing pad strip can be achieved easily and expeditiously thereby minimizing the length of time needed to take the polishing system off-line thus having minimal effect on the throughput. Accordingly, the apparatus and the methods of the present invention provide for polishing surface layers of a wafer using a polishing pad that is less expensive to maintain and is more effectively serviced after its use degrades the effectiveness of the polishing.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.